The present invention relates to a carburetor for internal combustion engines with a fuel-carrying main injection system which discharges upstream from an arbitrarily actuated main throttle into the intake duct, and an idling mixture duct discharging downstream of this main throttle via an arbitrarily adjustable throttle cross section. From this idling mixture duct, a transit opening leads into the intake duct whose exit cross section upon opening the main throttle away from the idling position shifts from the intake duct section upstream of the main throttle to the section downstream of the main throttle. There is an auxiliary channel discharging into this region to add another amount of air-fuel mixture.
A carburetor with an idling duct transition opening whose cross section can be regulated is known from German Utility Pat. 19 66 970 published Feb. 26, 1976. This transition opening causes an additional mixture supply when changing from idling to slow speed, to obtain a perfect running of the internal combustion engine also for slow speed, without increasing the mixture supply during idling in a manner prohibited by the exhaust gas regulations. However, this known carburetor system does not permit independent adjustment of the mixture for idling and for slow speed. This means that every change in adjustment for one mode of operation results in a change of setting for the other mode of operation since the flow direction in the transition holes reverses when shifting from one mode to the other. In order to remedy this difficulty, the German Patent Specification 19 28 532 dated Aug. 12, 1968, provided an auxiliary system which has an arbitrarily adjusted air duct discharging in the region of the transition openings. Futhermore, a mixtureforming independent duct system with adjustment facilities was provided with the exit again in the region of the transition holes. This solves the problem of independent adjustment, but difficulties of another type arise. The proposal with the air duct has the disadvantage that the duct must have a rather large cross section in order to provide an effective intervention. Because of the space restrictions on a carburetor, design difficulties arise. Besides space requirement for several and partly long ducts, the additional duct system for mixture forming has the disadvantage that it is expensive to manufacture.
Accordingly, it is an object of the present invention to provide a carburetor which makes possible an independent setting of the idling system and of a transition system and which can be produced with a reduced space requirement and low expenditure.
Another obejct of the present invention is to provide a carburetor of the foregoing character which is substantially simple in construction and may be economically fabricated.
The further object of the present invention is to provide a carburetor, as described, which may be readily maintained in service and which has a substantially long operating life.